1. Field of the Invention
The invention to which this application relates is a broadcast data receiver apparatus which is provided in a form so as to have an improved response to long and short term fading of the data channels.
2. Prior Art
The demand for increased capacity in data receiving apparatus, and/or reduced information errors continues to grow and there is also an increasing demand for generally efficient operation of wireless communication systems. However, a fundamental constraint to the capacity of the data transmission and receiving system is one or both of the digital receiver and the propagation medium (i.e the channel on which the data is transmitted).
Broadcast signals which are transmitted are typically distorted by atmospheric and environmental impairments, thereby degrading the quality of the signal which is subsequently received. In general, one form of deterioration is fading which is typically caused by physical phenomena such as reflection, diffraction and scattering. According to the number of the scattering phenomena which may be present in a wireless channel, the effect of these phenomena is either rich or poor. This is the case in the occurrence of multipath and shadowing fading, respectively.
It is known from the theory of telecommunications that multipath fading and shadowing of propagated signals, (also known as short-term fading and long-term fading respectively), can be effectively described and represented by statistical distributions.
Conventionally used distributions such as those known as Rayleigh, Weibull and Nakagami -m, -n, -q distributions, are adequate when describing multipath fading. However, they are found not to be optimal and/or robust because they do not additionally consider the simultaneous occurrence of the shadowing effect.
Another known distribution known as the Suzuki statistical distribution has the advantage that it is a composite Rayleigh/Lognormal distribution. As a consequence, it is capable of describing at once both the multipath and the shadowing of communication signals which occur simultaneously during wireless propagation. However, the probability density function (PDF) of the Suzuki distribution is described by the integral of the synthesis of Lognormal and Rayleigh, distribution. An explicit solution to this integral is not known in the prior art and thus it has not been possible to implement a receiver for a digital data system which is operable over such a fading channel.
An existing method of compensating for shadowing is by providing the receiver with empirical data, i.e. actual data, relating to the geographical area in which the receiver is to be used. However, it, is time-consuming to produce such data, the data is not always specific enough to the receiver location, and if the receiver is moved to a new location, new empirical data has to be obtained.
An aim of the present invention is to provide a receiver which can characterise accurately the signal degradation caused by the presence of multipath fading and shadowing. Another aim is to provide a method whereby the characterisation of the signal degradation can be accurately determined.